A Message from the Vet - October 2012
Anesthesia, Part Two

Before surgery, it all starts with the physical exam and history. The exam allows us to start to assess the patient for anesthesia. First noted is the species, breed, age and sex of the pet. Each species we treat generally has a different anesthetic protocol; dogs, cats, birds, turtles, and fish are very different. Even within these groups, breed differences may dictate specific anesthesia protocols. For example, greyhounds require a higher oxygen flow than some; brachycephalic breeds (like English Bulldogs) have anatomical considerations before, during and after anesthesia; Dobermans have a greater risk of genetic bleeding disorders; and so on.

During the pre-surgical exam, we look at the patient's gum color and mucous membrane perfusion, listen to the heart and lungs, feel the femoral pulses, assess their personality (excitable, fearful, relaxed), palpate the abdomen for normality, assess parasite burden on the skin, and note physical abnormalities. We also ask questions about the pet, so that with your feedback, we can assess health issues that are obvious at home but not during the clinic exam: questions like has your pet developed an increase thirst, has there been a change in weight or food consumption, does your pet throw up, can he or she go for normal exercise, changes in bark, et cetera.

The next step is to assess what is going on inside your pet's body. That is why we recommend a blood test. Diabetes, liver disease, heart conduction disorders may effect how your pet reacts to anesthesia. Simple EKGs rule out some important heart problems. In some, x-rays may be necessary to assess risks and rewards and the procedure.

Once the pet is thoroughly examined and we have acquired the patient's information and history, we schedule the pet for the procedure. Fasting in animals prior to anesthesia is very important to minimize risk of regurgitation and compromise of breathing passages during the anesthesia and recovery. If your pet is under 16 weeks of age, prolonged fasting is not recommended due to the risk of low blood sugar.

On the day of the procedure, we check to ensure all our anesthesia equipment is working properly and prepare emergency drugs to be on hand.

Next we prepare the pet for anesthesia by giving a combination of medications that relax them, provide pain relief, and help the heart and respiratory tract cope with the effects of anesthesia. We also place an indwelling IV catheter. The catheter provides a port for delivery of anesthesia, supportive fluids for hydration or low blood pressure, and provides a route for emergency drugs in the infrequent instance of a crisis.

When the pre-anesthetic medications are in effect, we next deliver a carefully titrated dose of the induction agent. It is called the induction agent because it lasts a very short time and allows us to pass a breathing tube and start the controlled flow of anesthetic vapor mixed with oxygen. The transition from injectable anesthesia induction (propofol) to inhalant anesthesia maintenance (isoflurane and oxygen) occurs over the next several minutes. The induction of the anesthetic and the transition to long term inhalation is gradual and allows preparing and positioning of the patient.

The next step is to begin electrical monitoring the patient under anesthesia. Wires, clips and tubes are attached to your pet as soon as they enter the surgical suite. We monitor CO2, blood oxygenation, heart rate, respiratory rate, body temperature, blood pressure, and EKG. The technician actively records the readings from the monitor as well as constantly performs hands on monitoring of heart rate, respiratory rate, perfusion of tissues, and depth of anesthesia.

At the end of the anesthetic procedure, the pet is allowed to breathe pure oxygen to help "blow off" the anesthetic that is in the blood stream. Some of the anesthetic chemical is metabolized away by the body, while some of it is exhaled in each breath.

The patient is monitored continuously until the endotracheal tube is determined to be safe to remove. This is usually when the patient has recovered their swallow reflex. Once the breathing tube is removed, the stable patient is returned to the recovery area, and monitored until it is alert and assumes normal posturing.

Full recovery from the recumbent, unconscious pet to the standing, demanding-for-attention pet may be within minutes or hours.

There are many factors we take into consideration with our patients. Every patient is an individual, every anesthesia case is unique. We treat each one as the most important patient there is; we consider their well-being as important as if they were our own pet.

John Haddock, DVM

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